A unified state boundary surface that defines the upper limit of the specific volume of saturated clay and sand is first derived. It is extended to unsaturated soils by applying Bishop’s effective stress and using the effective degree of saturation as an independent state variable. Then, a critical state model for unsaturated clay and sand is formulated based on the unified state boundary surface. The model combines a rational soil–water characteristic curve incorporating packing density and hydraulic hysteresis. The model is validated by comparing the calculated results and results of extensive experiments, including one-dimensional and isotropic compression tests, triaxial shearing tests, and soaking-collapse tests under isotropic and anisotropic stress conditions on sand, clay, and mixed soil under saturated and unsaturated conditions. The proposed unified soil model presents a noble and universal framework for the rational description of broad soils’ behavior, in which the state boundary surface plays a central role. The model accurately predicts the compression, shearing, and soaking-induced collapse behaviors of various soil types in saturated and unsaturated conditions.

首先导出了定义饱和粘土和砂的比容上限的统一状态边界表面。通过应用 Bishop 有效应力并将有效饱和度作为独立状态变量，将其扩展到非饱和土。然后，基于统一的状态边界面，建立了非饱和粘土和砂的临界状态模型。该模型结合了合理的土壤-水特征曲线，其中包含填充密度和水力滞后。通过比较计算结果和大量实验的结果来验证该模型，包括在饱和和饱和条件下对沙子、粘土和混合土进行各向同性和各向异性应力条件下的一维和各向同性压缩试验、三轴剪切试验和浸泡-倒塌试验。不饱和条件。所提出的统一土壤模型为合理描述广泛的土壤行为提供了一个崇高而通用的框架，其中状态边界表面起着核心作用。该模型准确地预测了饱和和非饱和条件下各种土壤类型的压缩、剪切和浸泡引起的坍塌行为。